Add Magento SSR Observability Module

[digitalrisedorset]

Summary

Introduce a lightweight Magento observability module to capture SSR fragment lifecycle events and validate cache behaviour.

Motivation

SSR Fragment Cache introduces multiple execution paths:

Cache Hit
↓
Return Cached HTML

and

Cache Miss
↓
Generate SSR
↓
Store Fragment
↓
Return HTML

Without observability it becomes difficult to determine:

• Whether cache entries are being used
• Cache hit ratio
• SSR generation frequency
• Cache invalidation behaviour
• End-to-end SSR performance

Proposed Events

Cache Hit

ssr.cache.hit

Attributes:

widget
cache_key
fragment_size

Cache Miss

ssr.cache.miss

Attributes:

widget
cache_key

SSR Generation Started

ssr.generate.started

Attributes:

widget
cache_key

SSR Generation Completed

ssr.generate.completed

Attributes:

widget
cache_key
duration_ms
fragment_size

Cache Stored

ssr.cache.store

Attributes:

widget
cache_key
ttl
fragment_size

Expected Outcome

Enable validation of the complete SSR fragment journey through telemetry and provide visibility into cache effectiveness before wider rollout.